The Adzuma Laboratory is making an effort to understand the mechanisms of DNA recombination reactions. Their efforts are focused on the homologous recombination reaction catalyzed by RecA. MALDI-ion trap mass spectrometry was used to confirm a binding site of single stranded DNA on E. Coli RecA using photo-crosslinking. A paper describing analytical aspects of the determination of the site of crosslinking (Qin and Chait, Anal. Chem. 69,4002-4009, 1997).